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To the Editor The large register study by Narod et al1 reported breast cancer–specific mortality after a ductal carcinoma in situ (DCIS) diagnosis with special focus on the influence of initial treatment received. There are 2 methodological problems with this article.
First, by using the Kaplan-Meier approach to mortality curves (Figures 1 and 2, eFigures 1-8 in the Supplement) the authors essentially predicted the uninterpretable mortality in a world where all causes of death other than breast cancer were eliminated.2 The relevant target is the probability of dying of breast cancer before dying of other causes, estimable as the so-called cumulative incidence (see Falk et al3 for a correct analysis in a similar national study of DCIS from Norway, notably not cited by Narod et al1).
Keiding N, Opdahl S, Holmberg L. Treatment Recommendations for Patients With a Diagnosis of Ductal Carcinoma In Situ . JAMA Oncol. 2016;2(3):398. doi:10.1001/jamaoncol.2015.4863
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